2003 Vol. 20, No. 6
2003, 20(6): 1-6.
Abstract:
The physical and mechanical properties of hybrid reinforced rigid polyurethane composite foam were investigated with reinforcing agents of SiO2 particle and fibre. The effect of content of SiO2 and fibre on the properties of the PU composite foam was emphatically analysed, as well as the effect of length of fibre on its properties. The experiment results show that the tensile strength of the PU composite foam is optimal when the content of SiO2 is 20 wt% and the content of glass fibre is 7.8 wt%. The reinforcing effects of glass fibre, Nylon66 fibre and PAN-based carbon fibre were compared. The result shows that the tensile strength of the PU composite foam reinforced with 3 wt%~5 wt% carbon fibre is optimal.
The physical and mechanical properties of hybrid reinforced rigid polyurethane composite foam were investigated with reinforcing agents of SiO2 particle and fibre. The effect of content of SiO2 and fibre on the properties of the PU composite foam was emphatically analysed, as well as the effect of length of fibre on its properties. The experiment results show that the tensile strength of the PU composite foam is optimal when the content of SiO2 is 20 wt% and the content of glass fibre is 7.8 wt%. The reinforcing effects of glass fibre, Nylon66 fibre and PAN-based carbon fibre were compared. The result shows that the tensile strength of the PU composite foam reinforced with 3 wt%~5 wt% carbon fibre is optimal.
2003, 20(6): 7-10.
Abstract:
ODPA was used to replace BTDA in PMR-15, and PMDA was added into dianhydride. ODPA/PMDA-MDA PMR copolyimide resin system was synthesized with copolymerization. The resin-solution's viscosity, the processing property, the thermal-oxidation stability and flexural property of cured resins were characterized. The relationship between resin structure and the properties of the resin was also researched. The experimental results show that resin-solution's viscosity increases with increasing molecular weight and decreases with increasing PMDA content. Tg of resin decreases with increasing molecular weight and increases with increasing PMDA content. Softening temperature of resin increases with increasing molecular weight and PMDA content. The temperature of resin weight loss and flexural property change complexly.
ODPA was used to replace BTDA in PMR-15, and PMDA was added into dianhydride. ODPA/PMDA-MDA PMR copolyimide resin system was synthesized with copolymerization. The resin-solution's viscosity, the processing property, the thermal-oxidation stability and flexural property of cured resins were characterized. The relationship between resin structure and the properties of the resin was also researched. The experimental results show that resin-solution's viscosity increases with increasing molecular weight and decreases with increasing PMDA content. Tg of resin decreases with increasing molecular weight and increases with increasing PMDA content. Softening temperature of resin increases with increasing molecular weight and PMDA content. The temperature of resin weight loss and flexural property change complexly.
2003, 20(6): 11-15.
Abstract:
The adiabatic infiltration and the solidification/remelting of molten aluminum through a porous preform in a centrifugal force field are modeled numerically. The temperature and solid volume fraction profiles are presented for representative parameters. The numerical results show that the transient solidification and remelting in the centrifugal force field depend greatly on the infiltration kinetics and thermodynamics of the composite. The regional extent of the eutectic solid metal and its solid volume fraction increase with the moving of the infiltration front. The speed of the moving infiltration and remelting fronts decrease with the decreasing of porosity and rotational speed, but the speed difference between the moving fronts and the regional extend of the eutectic solid metal increases with the decreasing of porosity and decreases with the decreasing of rotational speed.
The adiabatic infiltration and the solidification/remelting of molten aluminum through a porous preform in a centrifugal force field are modeled numerically. The temperature and solid volume fraction profiles are presented for representative parameters. The numerical results show that the transient solidification and remelting in the centrifugal force field depend greatly on the infiltration kinetics and thermodynamics of the composite. The regional extent of the eutectic solid metal and its solid volume fraction increase with the moving of the infiltration front. The speed of the moving infiltration and remelting fronts decrease with the decreasing of porosity and rotational speed, but the speed difference between the moving fronts and the regional extend of the eutectic solid metal increases with the decreasing of porosity and decreases with the decreasing of rotational speed.
2003, 20(6): 16-20.
Abstract:
Many experimental phenomena show that the primary Si content affects the primary crystal silicon distribution in hypereutectic Al-Si alloy functionally gradient matrial (FGM) prepared by centrifugal casting. To control the distribution of the primary crystal silicon, the influence is studied. The critical primary Si content and critical temperature were gained by theoretical analysis. At the lower primary Si content or lower temperature than critical parameters, the density of the primary crystal silicon is lower than that of the remained Al-Si liquid alloy. When the primary Si content is higher than the critical content and the temperature is higher than the critical temperature, the density of the primary crystal silicon is higher than that of the remained liquid alloy. In the centrifugal force field, the primary crystal silicon in the hypereutectic Al-Si alloys, whose primary Si content is lower than the critical content, is assembled in the lining by the centrifugal force, and the primary crystal silicon in the high Si content hypereutectic Al-Si alloys, whose Si content is higher than the critical content, is assembled in outside and lining. The analysis agrees with the experiments.
Many experimental phenomena show that the primary Si content affects the primary crystal silicon distribution in hypereutectic Al-Si alloy functionally gradient matrial (FGM) prepared by centrifugal casting. To control the distribution of the primary crystal silicon, the influence is studied. The critical primary Si content and critical temperature were gained by theoretical analysis. At the lower primary Si content or lower temperature than critical parameters, the density of the primary crystal silicon is lower than that of the remained Al-Si liquid alloy. When the primary Si content is higher than the critical content and the temperature is higher than the critical temperature, the density of the primary crystal silicon is higher than that of the remained liquid alloy. In the centrifugal force field, the primary crystal silicon in the hypereutectic Al-Si alloys, whose primary Si content is lower than the critical content, is assembled in the lining by the centrifugal force, and the primary crystal silicon in the high Si content hypereutectic Al-Si alloys, whose Si content is higher than the critical content, is assembled in outside and lining. The analysis agrees with the experiments.
2003, 20(6): 21-25.
Abstract:
The surface flaws of different sizes were introduced into SiC/BN laminated ceramics by Vickers indentation method. The specimens were fractured by three-point bending. The effect of the surface flaw size on strength of SiC/BN ceramics was studied. The R-curve of SiC/BN laminated ceramics was evaluated using the indentation-strength method and compared with that of the monolithic SiC. The results show that the fracture strength for monolithic SiC decreases steeply with increasing indentation load, while for SiC/BN laminated ceramics reducing slightly with increasing indentation load, suggesting an exceptional damage resistance. Moreover, a rising R-curve behavior was demonstrated from the strength-indentation load method for SiC/BN laminated ceramics, a plateau R-curve behavior for monolithic SiC. The excellent damage resistance of SiC/BN laminated ceramics should be attributed to the crack deflection at the SiC/BN weak interfaces. The results show that SiC/BN laminated ceramics can retain a significant fraction of its strength under contact damage conditions; this should allow it to exhibit superior resistance to impact- or abrasion-induced damage in service.
The surface flaws of different sizes were introduced into SiC/BN laminated ceramics by Vickers indentation method. The specimens were fractured by three-point bending. The effect of the surface flaw size on strength of SiC/BN ceramics was studied. The R-curve of SiC/BN laminated ceramics was evaluated using the indentation-strength method and compared with that of the monolithic SiC. The results show that the fracture strength for monolithic SiC decreases steeply with increasing indentation load, while for SiC/BN laminated ceramics reducing slightly with increasing indentation load, suggesting an exceptional damage resistance. Moreover, a rising R-curve behavior was demonstrated from the strength-indentation load method for SiC/BN laminated ceramics, a plateau R-curve behavior for monolithic SiC. The excellent damage resistance of SiC/BN laminated ceramics should be attributed to the crack deflection at the SiC/BN weak interfaces. The results show that SiC/BN laminated ceramics can retain a significant fraction of its strength under contact damage conditions; this should allow it to exhibit superior resistance to impact- or abrasion-induced damage in service.
2003, 20(6): 26-30.
Abstract:
The friction and wear behavior of fly ash particles reinforced ZL109 composites prepared by the squeeze-casting method were investigated under various conditions. Under the lower loads and at the lower sliding speeds,the wear resistance of the MMCs is superior evidently to that of the Al matrix, and increases with the volume fraction of fly ash particles. The friction coefficient is steadily lower than that of Al matrix. The improvement of the wear resistance of the MMCs decreases under the higher loads and at the higher sliding speeds compared with Al matrix. But the friction coefficient of the MMCs could still keep a lower value. The reason is that the wear mechanisms in the MMCs have been transformed with increasing load and sliding speed. The transformation of wear mechanisms in MMCs was also investigated in the paper.
The friction and wear behavior of fly ash particles reinforced ZL109 composites prepared by the squeeze-casting method were investigated under various conditions. Under the lower loads and at the lower sliding speeds,the wear resistance of the MMCs is superior evidently to that of the Al matrix, and increases with the volume fraction of fly ash particles. The friction coefficient is steadily lower than that of Al matrix. The improvement of the wear resistance of the MMCs decreases under the higher loads and at the higher sliding speeds compared with Al matrix. But the friction coefficient of the MMCs could still keep a lower value. The reason is that the wear mechanisms in the MMCs have been transformed with increasing load and sliding speed. The transformation of wear mechanisms in MMCs was also investigated in the paper.
2003, 20(6): 31-35.
Abstract:
Titanium diboride-copper-nickel cermet was fabricated from titanium, boron, copper and nickel powders by combustion synthesis under conditions of pseudo hot isostatic pressing. The TiB2-Cu-Ni cermet was heated by using a plasma torch to investigate the thermal shock resistance and ablation behaviour. The microstructures of the cermet pre- and post-ablation were examined by SEM, EPMA and EDX. The result shows that the thermal shock resistance of the cermet is good, and the cermet does not burst apart when the material is instantly heated. However, a macro-crack is immediately formed on the surface of cermet when the ablation is just over. The mass loss of cermet after ablation for 20 s is 0.9 g and the mass loss ratio is 0.045g/s, which shows a good ablation property of the material. The ablation mechanism of TiB2-Cu-Ni cermet is the volatilization of metal binder, hot chemical ablation and mechanical erosion.
Titanium diboride-copper-nickel cermet was fabricated from titanium, boron, copper and nickel powders by combustion synthesis under conditions of pseudo hot isostatic pressing. The TiB2-Cu-Ni cermet was heated by using a plasma torch to investigate the thermal shock resistance and ablation behaviour. The microstructures of the cermet pre- and post-ablation were examined by SEM, EPMA and EDX. The result shows that the thermal shock resistance of the cermet is good, and the cermet does not burst apart when the material is instantly heated. However, a macro-crack is immediately formed on the surface of cermet when the ablation is just over. The mass loss of cermet after ablation for 20 s is 0.9 g and the mass loss ratio is 0.045g/s, which shows a good ablation property of the material. The ablation mechanism of TiB2-Cu-Ni cermet is the volatilization of metal binder, hot chemical ablation and mechanical erosion.
2003, 20(6): 36-41.
Abstract:
The compressive plastic deformation of particle-reinforced metal-matrix composites was investigated through numerical modeling at high strain rates. The numerical modeling is performed using axisymmetric unit cell model, with the particles treated as elastic ellipsoids or cylinders embedded within a visco-plastic matrix. Five particle volume fractions from 10% to 50% and three aluminium matrix materials LY12CZ, LC4 and 7075 were analyzed. The results show that the flow stress increases with the increasing of strain rate and the volume fraction of the reinforcement. The flow stress increases more for the higher strain hardening matrix material and for the cylindrical reinforcement. The strain rate sensitivity is also related to the matrix material and the particle shape. A simple analytical model is introduced which is able to describe the features of the computational predictions to a certain extent, which is in good agreement with the experimental results.
The compressive plastic deformation of particle-reinforced metal-matrix composites was investigated through numerical modeling at high strain rates. The numerical modeling is performed using axisymmetric unit cell model, with the particles treated as elastic ellipsoids or cylinders embedded within a visco-plastic matrix. Five particle volume fractions from 10% to 50% and three aluminium matrix materials LY12CZ, LC4 and 7075 were analyzed. The results show that the flow stress increases with the increasing of strain rate and the volume fraction of the reinforcement. The flow stress increases more for the higher strain hardening matrix material and for the cylindrical reinforcement. The strain rate sensitivity is also related to the matrix material and the particle shape. A simple analytical model is introduced which is able to describe the features of the computational predictions to a certain extent, which is in good agreement with the experimental results.
2003, 20(6): 42-46.
Abstract:
The optimum component distribution, which includes the thickness of each layer, the number of layers and the component distribution gene, is enacted by means of finite element analysis. Based on the calculations, the optimized PSZ/Mo functionally gradient materials were synthesized using the hot pressing method. Then the thermal shock experiment is carried out using the thermal properties testing equipment which was developed by ourselves. Based on the data from the thermal shock experiment, the temperature distribution and thermal stress under steady heat insulation in the optimized component distribution PSZ/Mo functionally gradient materials were calculated to explain why the optimized samples have so good thermal shock resistance properties.
The optimum component distribution, which includes the thickness of each layer, the number of layers and the component distribution gene, is enacted by means of finite element analysis. Based on the calculations, the optimized PSZ/Mo functionally gradient materials were synthesized using the hot pressing method. Then the thermal shock experiment is carried out using the thermal properties testing equipment which was developed by ourselves. Based on the data from the thermal shock experiment, the temperature distribution and thermal stress under steady heat insulation in the optimized component distribution PSZ/Mo functionally gradient materials were calculated to explain why the optimized samples have so good thermal shock resistance properties.
2003, 20(6): 47-51.
Abstract:
This paper presents test results on the mechanical and self-sensing properties of CFRP bars and concrete beams reinforced with CFRP bars. The CFRP bars were produced in different diameters and with different surface treatments. Eighteen CFRP bar specimens in three series are tested for elastic modulus, ultimate tensile strength and electrical resistance change. Six concrete beams reinforced with CFRP bars under third-point loading were tested. The curves of electrical resistance change of CFRP bars in concrete beams versus load were presented. The test results show that CFRP bars can be used as reinforcement and monitor the concrete structures mechanical properties.
This paper presents test results on the mechanical and self-sensing properties of CFRP bars and concrete beams reinforced with CFRP bars. The CFRP bars were produced in different diameters and with different surface treatments. Eighteen CFRP bar specimens in three series are tested for elastic modulus, ultimate tensile strength and electrical resistance change. Six concrete beams reinforced with CFRP bars under third-point loading were tested. The curves of electrical resistance change of CFRP bars in concrete beams versus load were presented. The test results show that CFRP bars can be used as reinforcement and monitor the concrete structures mechanical properties.
2003, 20(6): 52-56.
Abstract:
Hydroxyapatite(HA)powder and 20 wt% titanium powder were mixed and sintered to prepare sputtering target. A TiO2/HA bio-composite film was deposited on the substrate of pure titanium by RF magnetron sputtering. Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and difference temperature analysis (DTA) were used to characterize the as-sputtered films. At the same time, the re-crystallized technique of sputtered films was also investigated. The results show that the sputtered film consists of TiO2 particles and amorphous phase of calcium phosphate, and the Ca/P ratio is lower than that of HA (Ca/P=1.67) because of elective sputtering and loss of OH-. The amorphous phase of calcium phosphate is re-crystallized entirely and re-changed into HA partly by water vapour-treating at 700℃ for 0.5 h. There is no micro-crack in the interface between Ti metal and sputtered film treated with water vapour.
Hydroxyapatite(HA)powder and 20 wt% titanium powder were mixed and sintered to prepare sputtering target. A TiO2/HA bio-composite film was deposited on the substrate of pure titanium by RF magnetron sputtering. Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and difference temperature analysis (DTA) were used to characterize the as-sputtered films. At the same time, the re-crystallized technique of sputtered films was also investigated. The results show that the sputtered film consists of TiO2 particles and amorphous phase of calcium phosphate, and the Ca/P ratio is lower than that of HA (Ca/P=1.67) because of elective sputtering and loss of OH-. The amorphous phase of calcium phosphate is re-crystallized entirely and re-changed into HA partly by water vapour-treating at 700℃ for 0.5 h. There is no micro-crack in the interface between Ti metal and sputtered film treated with water vapour.
2003, 20(6): 57-60.
Abstract:
Ti/HA composites were manufactured by spark plasma sintering (SPS). The microstructure,density and the pH value were studied for Ti/HA samples with different proportions. The biological hemolytic experiment was done. The result indicates that the relative density of 50％Ti-50％HA composite increases from 73％ to 94.4％ while the particles are passivated before sintering, the pH value remains neutral and the biological hemolytic experiment index is 4%, which meets the demand of bioactivity materials.
Ti/HA composites were manufactured by spark plasma sintering (SPS). The microstructure,density and the pH value were studied for Ti/HA samples with different proportions. The biological hemolytic experiment was done. The result indicates that the relative density of 50％Ti-50％HA composite increases from 73％ to 94.4％ while the particles are passivated before sintering, the pH value remains neutral and the biological hemolytic experiment index is 4%, which meets the demand of bioactivity materials.
2003, 20(6): 61-66.
Abstract:
In order to develop the light-weight biological composite structures, the fore wing structures of beetles, Allomyrina dichotoma, were investigated. As a result, the structural models for both fore-wing of the beetle and trabecular structure were established: (1) the allomyrina dichotoma fore-wing is of sandwich plate structure with the central void layer of trabeculae, and this is one of the typical light-weight composite structures; (2) chitin fibers in trabeculae curved more than 90 degree to connect to the chitin fiber on the upper and the lower lamination, and it is clear that this structure will increase peeling resistance greatly for the laminated composite structures.
In order to develop the light-weight biological composite structures, the fore wing structures of beetles, Allomyrina dichotoma, were investigated. As a result, the structural models for both fore-wing of the beetle and trabecular structure were established: (1) the allomyrina dichotoma fore-wing is of sandwich plate structure with the central void layer of trabeculae, and this is one of the typical light-weight composite structures; (2) chitin fibers in trabeculae curved more than 90 degree to connect to the chitin fiber on the upper and the lower lamination, and it is clear that this structure will increase peeling resistance greatly for the laminated composite structures.
2003, 20(6): 67-72.
Abstract:
The mechanical properties of three dimensional and four-direction braided composites were investigated by the macroscopic compressive experiments, and the SEM analysis was performed for the fracture surface of specimens to understand the compressive failure mechanism of this kind of composite. The experimental results show that the longitudinal modulus is much larger than the transverse one, and the most important parameter to affect the longitudinal compressive properties of the composites is the braided angle. The mechanism of longitudinal compressive failure of the composites changes with the increase of the braided angles. When the braided angle is smaller, the material behaves as the brittle characteristics. But if the braided angle is larger than a certain critical one, the stress-strain curves of the materials approach nonlinear ones and the ductility of the composites increases, behaving mostly as the characteristics of plastic failure. In addition, the mechanism of transverse compressive failure of the composites is significantly different from the one of longitudinal compression.
The mechanical properties of three dimensional and four-direction braided composites were investigated by the macroscopic compressive experiments, and the SEM analysis was performed for the fracture surface of specimens to understand the compressive failure mechanism of this kind of composite. The experimental results show that the longitudinal modulus is much larger than the transverse one, and the most important parameter to affect the longitudinal compressive properties of the composites is the braided angle. The mechanism of longitudinal compressive failure of the composites changes with the increase of the braided angles. When the braided angle is smaller, the material behaves as the brittle characteristics. But if the braided angle is larger than a certain critical one, the stress-strain curves of the materials approach nonlinear ones and the ductility of the composites increases, behaving mostly as the characteristics of plastic failure. In addition, the mechanism of transverse compressive failure of the composites is significantly different from the one of longitudinal compression.
2003, 20(6): 73-79.
Abstract:
The stress redistribution of fibers immediately adjacent is examined to a broken high modulus fiber in an intermingled hybrid composite. The problem was formulated by establishing the proper analysis model, and the solutions of two-dimensional elastic mechanics in conjunction with the Fourier transform were adopted to set up the singular integral equations for this problem. From the solution of these equations, the stress concentration factors(SCF) were evaluated for the high and low modulus fibers and matrix. The numerical analysis results provide a theoretical explanation of the observed"hybrid effect".Compared with the existing Shear-Lag theory results, the present analysis results are more accurate and reasonable, and can be used in the design of intermingled hybrid composites.
The stress redistribution of fibers immediately adjacent is examined to a broken high modulus fiber in an intermingled hybrid composite. The problem was formulated by establishing the proper analysis model, and the solutions of two-dimensional elastic mechanics in conjunction with the Fourier transform were adopted to set up the singular integral equations for this problem. From the solution of these equations, the stress concentration factors(SCF) were evaluated for the high and low modulus fibers and matrix. The numerical analysis results provide a theoretical explanation of the observed"hybrid effect".Compared with the existing Shear-Lag theory results, the present analysis results are more accurate and reasonable, and can be used in the design of intermingled hybrid composites.
2003, 20(6): 80-86.
Abstract:
Using an approximate analytical method, the explicit expression of stress concentration factors is derived for an eccentric circular hole in a tension orthotropic finite-width strip. The accuracy of the expression is adequate except some extreme situations. The error estimate is based on a comparison with the results from finite element analysis. When the eccentricity is taken as zero, i.e. for the simplified case of a center circular hole in a tension orthotropic finite-width strip, the deduced expression has good accuracy, as demonstrated by agreement with values from the references and finite element analysis. It is shown that the formulation method and the derived expressions can be used to solve difficult problems of stress concentration factors for anisotropic materials, although they are quite simple.
Using an approximate analytical method, the explicit expression of stress concentration factors is derived for an eccentric circular hole in a tension orthotropic finite-width strip. The accuracy of the expression is adequate except some extreme situations. The error estimate is based on a comparison with the results from finite element analysis. When the eccentricity is taken as zero, i.e. for the simplified case of a center circular hole in a tension orthotropic finite-width strip, the deduced expression has good accuracy, as demonstrated by agreement with values from the references and finite element analysis. It is shown that the formulation method and the derived expressions can be used to solve difficult problems of stress concentration factors for anisotropic materials, although they are quite simple.
2003, 20(6): 87-91.
Abstract:
The method of tension winding of fiber bundle is an effective way to improve the radial strength of flywheels. An approach of calculating the initial stress and deformation in tension winding according to misfit is advanced. The results show that the hoop stress decreases firstly and then increases while the radial compression stress decreases all the while in the qually winding tension. While in changed winding tension which is enhanced from lower to higher levels, the radial compression stress can be increased. It is not sufficient to use tension winding only in flywheel design. The tension winding and process of pressfit should be used together to design the rational initial radial compression stress.
The method of tension winding of fiber bundle is an effective way to improve the radial strength of flywheels. An approach of calculating the initial stress and deformation in tension winding according to misfit is advanced. The results show that the hoop stress decreases firstly and then increases while the radial compression stress decreases all the while in the qually winding tension. While in changed winding tension which is enhanced from lower to higher levels, the radial compression stress can be increased. It is not sufficient to use tension winding only in flywheel design. The tension winding and process of pressfit should be used together to design the rational initial radial compression stress.
2003, 20(6): 92-97.
Abstract:
A confocal ellipsoid model is proposed to predict the effective moduli of the composites with three-dimensional randomly oriented inclusions. The change of inclusion's distribution due to the increase of the inclusion's volume fraction is taken into account. The analytical expressions of the effective shear and bulk moduli are given, and they are compared with those predicted by Mori-Tanaka(MT) method,Ponte-Castaneda-Willis(PCW) method and Hashin-Shtrikman(HS)bounds. The results show that the prediction of the present method is between the results of the MT method and the PCW method. In addition, the influence of different orientational averaging methods on the effective moduli of composites is also discussed.
A confocal ellipsoid model is proposed to predict the effective moduli of the composites with three-dimensional randomly oriented inclusions. The change of inclusion's distribution due to the increase of the inclusion's volume fraction is taken into account. The analytical expressions of the effective shear and bulk moduli are given, and they are compared with those predicted by Mori-Tanaka(MT) method,Ponte-Castaneda-Willis(PCW) method and Hashin-Shtrikman(HS)bounds. The results show that the prediction of the present method is between the results of the MT method and the PCW method. In addition, the influence of different orientational averaging methods on the effective moduli of composites is also discussed.
2003, 20(6): 98-103.
Abstract:
The surface of UHMWPE fiber was treated by a low temperature plasma. After the plasma treatment, the wetting power of UHMWPE fiber to ethylene glycol is improved and the contact angle is reduced. The active free radicals are produced on the fiber surface and the absorbability to methene blue is enhanced. The plasma treatment makes the fiber increase the oxygen content and surface area. The ILSS of UHMWPE/epoxy composite is enhanced more than 3 times.
The surface of UHMWPE fiber was treated by a low temperature plasma. After the plasma treatment, the wetting power of UHMWPE fiber to ethylene glycol is improved and the contact angle is reduced. The active free radicals are produced on the fiber surface and the absorbability to methene blue is enhanced. The plasma treatment makes the fiber increase the oxygen content and surface area. The ILSS of UHMWPE/epoxy composite is enhanced more than 3 times.
2003, 20(6): 104-108.
Abstract:
The quasi-static and high strain rate tensile impact experiments on the high-strength and high-modulus polyethylene fiber (HSM-PE) yarns were performed at 20℃~110℃ and strain rate 0.001/s~700/s by means of MTS 810, rotating disk bar-bar tensile impact apparatus and temperature-controlled box, and the stress-strain curves of fiber yarns at different temperatures and different strain rates were obtained. The experimental results indicate that the initial elastic modulus of Dyneema SK65 fiber yarns is rate-dependent and temperature-dependent:it increases with the rising of strain rate and decreases with the rising of testing temperature. The strength of the fiber yarns tested from quasi-static to dynamic is rate-dependent at the normal temperature, but it is rate-insensitive at high strain rate and at 20℃~110℃. The unstable strain is also rate-dependent and temperature-dependent: it decreases with the rising of the strain rate and increases with the rising of the testing temperature. The fracture strain energy density at the high strain rate is mainly determined by the initial elastic modulus and the unstable strain and affected by the temperature and the strain rate.
The quasi-static and high strain rate tensile impact experiments on the high-strength and high-modulus polyethylene fiber (HSM-PE) yarns were performed at 20℃~110℃ and strain rate 0.001/s~700/s by means of MTS 810, rotating disk bar-bar tensile impact apparatus and temperature-controlled box, and the stress-strain curves of fiber yarns at different temperatures and different strain rates were obtained. The experimental results indicate that the initial elastic modulus of Dyneema SK65 fiber yarns is rate-dependent and temperature-dependent:it increases with the rising of strain rate and decreases with the rising of testing temperature. The strength of the fiber yarns tested from quasi-static to dynamic is rate-dependent at the normal temperature, but it is rate-insensitive at high strain rate and at 20℃~110℃. The unstable strain is also rate-dependent and temperature-dependent: it decreases with the rising of the strain rate and increases with the rising of the testing temperature. The fracture strain energy density at the high strain rate is mainly determined by the initial elastic modulus and the unstable strain and affected by the temperature and the strain rate.
2003, 20(6): 109-114.
Abstract:
A statistical model is developed to study the flowing performance of resin fluid inside fibrous assemblies during the impregnation process. The probability of a fluid move is the function of the variation of a fiber/resin system's energy before and after moving. The energy of the fiber/resin system includes its internal energy, which is the Hamiltonian, and the work done by the interfacial tension between the fiber and resin, by the pressure driving the resin, and by the friction loss when the resin flows through fibrous assemblies, which is expressed in thermodynamic terms as pressure. Simulation is performed to study the performances of a selected fluid flows through fibrous assemblies, i.e. water through nonwoven PET fiber mats and unsaturated polyester resin through glass woven fabrics. To verify the model, a set of experiments illustrates the water through the fiber mats with different fiber volume fractions and the resin through the woven fabric with different influxes. Simulation results are in good agreement with experiments, indicating good prospect of the model used in this area.
A statistical model is developed to study the flowing performance of resin fluid inside fibrous assemblies during the impregnation process. The probability of a fluid move is the function of the variation of a fiber/resin system's energy before and after moving. The energy of the fiber/resin system includes its internal energy, which is the Hamiltonian, and the work done by the interfacial tension between the fiber and resin, by the pressure driving the resin, and by the friction loss when the resin flows through fibrous assemblies, which is expressed in thermodynamic terms as pressure. Simulation is performed to study the performances of a selected fluid flows through fibrous assemblies, i.e. water through nonwoven PET fiber mats and unsaturated polyester resin through glass woven fabrics. To verify the model, a set of experiments illustrates the water through the fiber mats with different fiber volume fractions and the resin through the woven fabric with different influxes. Simulation results are in good agreement with experiments, indicating good prospect of the model used in this area.
ELECTRIC ENTHALPY OF PIEZOELECTRIC MATERIALS AND COUPLING ANALYSIS OF MECHANICAL AND ELECTRIC FIELDS
2003, 20(6): 115-120.
Abstract:
This paper presents the electric enthalpy density-based Hamilton principle and its application in solving the problems with coupled mechanical and electrical properties of piezoelectric materials. The analytical solutions are derived for the deformations and electric potential of two simple structures. The resulting solutions are compared with the existing results, and the errors in these results are pointed out. The results demonstrate that the electric enthalpy-based Hamilton principle is a simple and powerful model to solve electric-mechanical coupling problems of piezoelectric materials. The model presented here can be also used for the mathematical model of finite element analysis of piezoelectric materials and structures.
This paper presents the electric enthalpy density-based Hamilton principle and its application in solving the problems with coupled mechanical and electrical properties of piezoelectric materials. The analytical solutions are derived for the deformations and electric potential of two simple structures. The resulting solutions are compared with the existing results, and the errors in these results are pointed out. The results demonstrate that the electric enthalpy-based Hamilton principle is a simple and powerful model to solve electric-mechanical coupling problems of piezoelectric materials. The model presented here can be also used for the mathematical model of finite element analysis of piezoelectric materials and structures.
2003, 20(6): 121-124.
Abstract:
Tetrapod-shaped ZnO (T-ZnO) whiskers with high purity were prepared by using a carbon-reducing agent control method in a short time. The products were characterized with optical microscope, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. It is demonstrated that the product is the pure zinc oxide with a structure of hexagonal cross sections, and that the tetrapod-shaped ZnO whiskers have the performance of dielectrical dissipation materials in the microwave electromagnetic experiment. The tetrapod-shaped ZnO whiskers would be a candidate for the microwave absorbing material.
Tetrapod-shaped ZnO (T-ZnO) whiskers with high purity were prepared by using a carbon-reducing agent control method in a short time. The products were characterized with optical microscope, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. It is demonstrated that the product is the pure zinc oxide with a structure of hexagonal cross sections, and that the tetrapod-shaped ZnO whiskers have the performance of dielectrical dissipation materials in the microwave electromagnetic experiment. The tetrapod-shaped ZnO whiskers would be a candidate for the microwave absorbing material.
2003, 20(6): 125-129.
Abstract:
The working principles and properties of a friction tester developed by the authors the are introduced for heavy load. The loading maximum value is 1000 kN. The varying ranges of its velocity are wide. The relationship between the friction coefficient and bearing capacity of the braided composites was explored at 2.5 r/min. Its friction time effect was measured. While the spherical bearing capacity of bearings was 135 MPa, the wear curve of bearings was measured. The relationship between temperature of bearings and continuous rotating time was explored. The curves of the friction coefficient varying with the continuous rotating time were measured. The results show that the dry friction coefficient is 0.038~0.061 when the load-carrying capacity of braided PTFE spherical bearings is 25~135 MPa. The mechanism of bearings' failure was analyzed by means of scanning electron microscopy. The PTFE of the braided composite is extruded in the process of the wear test. The self-lubricating function of spherical bearings is going down. The base of the braided composite is worn away.
The working principles and properties of a friction tester developed by the authors the are introduced for heavy load. The loading maximum value is 1000 kN. The varying ranges of its velocity are wide. The relationship between the friction coefficient and bearing capacity of the braided composites was explored at 2.5 r/min. Its friction time effect was measured. While the spherical bearing capacity of bearings was 135 MPa, the wear curve of bearings was measured. The relationship between temperature of bearings and continuous rotating time was explored. The curves of the friction coefficient varying with the continuous rotating time were measured. The results show that the dry friction coefficient is 0.038~0.061 when the load-carrying capacity of braided PTFE spherical bearings is 25~135 MPa. The mechanism of bearings' failure was analyzed by means of scanning electron microscopy. The PTFE of the braided composite is extruded in the process of the wear test. The self-lubricating function of spherical bearings is going down. The base of the braided composite is worn away.
2003, 20(6): 130-136.
Abstract:
The propagation characteristic of ultrasonic longitudinal guided waves in composite pipes is investigated. The dispersion characteristics were computed on the assumption that the frequency is a real number and the wavenumber is a complex number. The displacement amplitude component distributions were analyzed in a two-layer system. The optimal location, optimal mode and its frequency-thickness products of testing were chosen by the displacement amplitude component distributions. The results show that the values of the radial and axial displacements of guided waves are larger at the inner wall than those at the middle and outer walls of a two-layer composite pipe. When frequency-thickness products increase to a certain value, which will increase with the increasing of the order of mode, the radial and axial displacements approach zero. It should be the choice of frequency-thickness products where there are smaller radial displacement and larger axial displacement in testing of guided wave modes.
The propagation characteristic of ultrasonic longitudinal guided waves in composite pipes is investigated. The dispersion characteristics were computed on the assumption that the frequency is a real number and the wavenumber is a complex number. The displacement amplitude component distributions were analyzed in a two-layer system. The optimal location, optimal mode and its frequency-thickness products of testing were chosen by the displacement amplitude component distributions. The results show that the values of the radial and axial displacements of guided waves are larger at the inner wall than those at the middle and outer walls of a two-layer composite pipe. When frequency-thickness products increase to a certain value, which will increase with the increasing of the order of mode, the radial and axial displacements approach zero. It should be the choice of frequency-thickness products where there are smaller radial displacement and larger axial displacement in testing of guided wave modes.
2003, 20(6): 137-141.
Abstract:
Based on the theory of elastic dynamics, the scattering of elastic waves and the dynamic stress concentration in a fiber-reinforced composite are studied. The non-homogeneous region of interlayer is modeled to have many same-thickness layers with elastic properties. Analytical expressions of elastic waves in different medium regions are presented. The unknown coefficients of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of the interfaces. The expressions for calculating the dynamic stress concentration factors are given. As examples, the numerical results of dynamic stress concentration factors near the interfaces of two kinds of fiber-reinforced composites, namely, SiC-fiber-reinforced Ti composite and Al2O3-fiber-reinforced Al composite, are calculated. The influences of material characters and structural size on the dynamic stress concentration factors near the interfaces of these two kinds of composites are analyzed.
Based on the theory of elastic dynamics, the scattering of elastic waves and the dynamic stress concentration in a fiber-reinforced composite are studied. The non-homogeneous region of interlayer is modeled to have many same-thickness layers with elastic properties. Analytical expressions of elastic waves in different medium regions are presented. The unknown coefficients of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of the interfaces. The expressions for calculating the dynamic stress concentration factors are given. As examples, the numerical results of dynamic stress concentration factors near the interfaces of two kinds of fiber-reinforced composites, namely, SiC-fiber-reinforced Ti composite and Al2O3-fiber-reinforced Al composite, are calculated. The influences of material characters and structural size on the dynamic stress concentration factors near the interfaces of these two kinds of composites are analyzed.
2003, 20(6): 142-146.
Abstract:
The CNTs-(Ni-P) composites were prepared by electroless plating on 45# steel substrate, and the optimum composition and operating conditions were obtained. The TEM was used to observe the CNTs' structure,the SEM was used to observe the appearance and distribution of the CNTs in the composites and the AFM(atomic force microscopy) was used to analyze the roughness status of the composite surface. The influence of the CNTs on the tribological performance of the composites is discussed. The results show that the CNTs-(Ni-P) composites have better wear-resistance than the uncoated substrate and the substrate coated with nikel.
The CNTs-(Ni-P) composites were prepared by electroless plating on 45# steel substrate, and the optimum composition and operating conditions were obtained. The TEM was used to observe the CNTs' structure,the SEM was used to observe the appearance and distribution of the CNTs in the composites and the AFM(atomic force microscopy) was used to analyze the roughness status of the composite surface. The influence of the CNTs on the tribological performance of the composites is discussed. The results show that the CNTs-(Ni-P) composites have better wear-resistance than the uncoated substrate and the substrate coated with nikel.
2003, 20(6): 147-150.
Abstract:
The fiber/matrix interfacial shear stress in the single-fiber reinforced composite was studied by photo-elastic experiment and the finite element method (FEM). Three different load levels were considered. It is found that the interfacial shear stress has a maximum value nearby the embedded top of the fiber/matrix interface. Along the fiber embedded length direction, the interfacial shear stress decreases quickly until it reaches a minimum value in the middle of the fiber. At the end of the fiber, there is a little increasing of the interfacial shear stress. It can be proved that the interfacial stress transformation from fiber to matrix or from matrix to fiber is mainly focused on the region of the embedded top of the fiber/matrix interface, where the interfacial shear stress reaches the critical stress first. In this region, the crack will initiate. Comparing the result of photoelastic experiment with the calculation of FEM simulation, both have the similar interfacial shear stress distribution.
The fiber/matrix interfacial shear stress in the single-fiber reinforced composite was studied by photo-elastic experiment and the finite element method (FEM). Three different load levels were considered. It is found that the interfacial shear stress has a maximum value nearby the embedded top of the fiber/matrix interface. Along the fiber embedded length direction, the interfacial shear stress decreases quickly until it reaches a minimum value in the middle of the fiber. At the end of the fiber, there is a little increasing of the interfacial shear stress. It can be proved that the interfacial stress transformation from fiber to matrix or from matrix to fiber is mainly focused on the region of the embedded top of the fiber/matrix interface, where the interfacial shear stress reaches the critical stress first. In this region, the crack will initiate. Comparing the result of photoelastic experiment with the calculation of FEM simulation, both have the similar interfacial shear stress distribution.
2003, 20(6): 151-154.
Abstract:
Continuous-fiber-reinforced Cu matrix composites were fabricated based on the electrochemical infiltration technique (ECI). The experimental results show that the dense fiber/Cu composites have been obtained on the present condition, which possess good mechanical properties. The fracture surface morphology and microstructures of the composites have been observed by SEM. It is indicated that the interfacial bond between fibers and Cu matrix is very well and the fibers do not have any damage. The ECI is feasible to prepare rapidly fiber-reinforced metal matrix composites at room temperature.
Continuous-fiber-reinforced Cu matrix composites were fabricated based on the electrochemical infiltration technique (ECI). The experimental results show that the dense fiber/Cu composites have been obtained on the present condition, which possess good mechanical properties. The fracture surface morphology and microstructures of the composites have been observed by SEM. It is indicated that the interfacial bond between fibers and Cu matrix is very well and the fibers do not have any damage. The ECI is feasible to prepare rapidly fiber-reinforced metal matrix composites at room temperature.
